1. Field of the Invention
The present invention relates generally to a coarse/fine adjustment of a rotary body and, more particularly, to a coarse/fine adjustment capable of coarsely finely adjusting a turn table or the like of a collimation telescope of a surveying instrument and a microscope by use of a single piece of manipulation knob.
2. Related Background Art
The conventional technology will be explained by exemplifying a surveying instrument.
The conventional surveying instrument incorporates a variety of fine adjustments into a rotary adjusting mechanism of a horizonal shaft or a perpendicular shaft in order to collimate the telescope with a high precision. The following is a mechanism proposed as a structure of this type of fine adjustment. A micromotion shaft is moved by transforming a rotation of a micromotion knob into a movement in the axial direction of a micromotion shaft. This micromotion shaft thrusts a projection part of a clamped ring attached to a rotary shaft such as a perpendicular shaft or the like of the surveying instrument. Thus, the rotary shaft makes a rotational micromotion (Japanese Utility Model Publication Nos. 1-34151 and 3-23524).
By the way, in those rotary shaft fine adjustments, the telescope is substantially manually directed beforehand to an object for collimation. The rotary shaft of the telescope is clamped in this state. Further, a micromotion of the rotary shaft is thus adjusted. Under such circumstances, a coarse adjustment is mounted in combination when automating the collimation of the telescope of the surveying instrument by driving an electric motor, etc. The fine adjustment is driven after driving the coarse adjustment. It is required that the telescope be collimated under proper motor control.
FIG. 7 is a plan view showing one example of the coarse adjustment described above. Referring to FIG. 7, the numeral 50 indicates a body of the surveying instrument. A rotary shaft 51 is rotatably supported on a rotary shaft bearing 52 substantially in the central position of a cylindrical part 50a of the body 50. A worm wheel 53 is fitted to the outer periphery of a flange 52a formed on this rotary shaft bearing 52.
On the other hand, a worm 54 meshing with this worm wheel 53 is accommodated in a breadth-expanded part 50b extending to assume an angular shape in some portion of the body 50. This worm 54 is tightly fitted to a rotary driving shaft 55 rotatably supported on bearings 154, 154 fixed to the side surfaces of the breadth-expanded part 50 b. Coarse motion knobs 56, 56 are secured to both ends of the rotary driving shaft 55. The rotary shaft 51 can be coarsely rotated in predetermined directions by turning the coarse knobs 56 forward or reversely.
A ratio of turn of the coarse knob to an angle of coarse rotation of the rotary shaft 51 can be set to a variety of values depending on a lead value of the worm 54 and a diameter of the worm wheel.
Incidentally, when employing a worm mechanism for driving under the motor control to collimate the telescope, it is impossible to set the screw lead of the worm to an infinitesimal width in terms of a working accuracy. Sufficient resolving power of the driving motor connected to the rotary driving shaft can not be drawn out. This results in such a problem that a collimating precision of the telescope declines.
Further, if the worm lead is set to the infinitesimal width, there arises an inconvenience in which the rotation knob has to be turned a considerable number of times when largely deflecting the telescope.
In this case, the fine adjustment described above is incorporated together with the coarse adjustment. The telescope can be also collimated by a combinational operation of the two adjustments. However, a plurality of mechanisms are accommodated in an interior of the body. Moreover, motors for driving these mechanisms are mounted. Consequently, the surveying instrument increases in size enough not to meet the user's demands for miniaturization as well as for a high performance.